DC plasma jet CVD method for producing diamond

ABSTRACT

A process for producing diamond includes a step of bringing a columnar cathode and a tubular pilot anode provided concentrically around the cathode, into proximity to a plasma jetting port of a front end portion of a tubular main anode provided concentrically around the pilot anode. According to the process, a voltage is applied across the cathode and the pilot anode to convert a pilot gas to the form of a plasma. Then, the cathode is moved away from the pilot anode along a common axis. The process also includes the step of holding the discharge voltage between the cathode and the pilot anode at a first preselected voltage, and then applying voltage across the cathode and the main anode to convert a main gas to the form of a plasma. Subsequently, at least the pilot anode is moved away from the main anode along the common axis while maintaining the discharge voltage between the cathode and the pilot anode at the first preselected voltage. The process further includes the steps of holding the discharge voltage between the cathode and the main anode at a second preselected voltage and jetting the main gas in the form of plasma from the jetting port while generating a main arc between the main anode and the cathode.

This application is a division of application Ser. No. 08/057,823 filedMay 7, 1993, now pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process and apparatus for productionof diamond, more particularly relates to a process and apparatus forproduction of diamond which performs gas phase synthesis of high qualitydiamond at a high speed.

2. Description of the Related Art

Diamond is the hardest material on earth, having a Vicker's hardness of10000. It also has a large Young's modulus and is superior in wearresistance and chemical stability. Due to these superior properties,diamond is an essential material in industry, in particular the hightech industries. Further, diamond has a heat conductivity of 2000 W/mK,four times that of copper, and is transparent in a wide range ofwavelength from the infrared to ultraviolet. Further, it is asemiconductor with a wide bandgap of 5.4 eV. Therefore, diamond isexpected to be put to use for heat sinks, heat radiating circuit boards,optical materials (window materials), heat resistant semiconductordevices, wear resistant coatings for tools and other objects, etc.

In recent years, there has been considerable research done in thesynthesis of diamond by the chemical vapor deposition method (CVDmethod). For commercial use of gas phase synthesized diamond, it isimportant to increase the speed of synthesis so as to reduce themanufacturing cost.

Many processes have been proposed as the process for gas phase synthesisof diamond. By the DC plasma jet CVD method developed by the presentinventors (see Japanese Unexamined Patent Publication (Kokai) No.64-33096), it is possible to synthesis diamond at a high production orfilm-forming speed of over 100 μm/hour.

FIG. 1 is a view for explaining the structure of a plasma torch of aconventional diamond producing apparatus.

In FIG. 1, 1 is circular columnar cathode with a printed front end, and2 is an anode provided so as to surround the cathode 1 with apredetermined clearance. By applying DC voltage between the cathode 1and the anode 2, an arc discharge is caused and reaction gas introducedin the clearance between the cathode 1 and anode 2 is converted toplasma in the clearance. Reference numeral 3 is a gas introduction portfor introduction of the reaction gas in the clearance between thecathode 1 and the anode 2.

When using a production apparatus having the above plasma torch tosynthesize diamond, a substrate 7 is placed at a position facing theplasma torch, reaction gas is introduced from the gas introduction port3 in the clearance between the cathode 1 and the anode 2, voltage isapplied between the cathode 1 and the anode 2 to cause an arc discharge,and the reaction gas introduced in the clearance is converted to plasma.Due to this, an arc column 5 is produced from the front end of thecathode 1 to the jetting port of the plasma jet 6 of the anode 2.

The plasma jet 6 is jetted from the jetting port of the front end of theplasma torch toward the substrate 7. This state is held for apredetermined time, whereby a diamond film 8 is formed on the substrate7.

In general, with a DC arc discharge, even with the same discharge power,if the arc column 5 is made longer, the discharge voltage raised, andthe discharge current lowered, there is less consumption of theelectrode material of the anode 2 and the rate of voltage fluctuationalso drops. Further, in synthesis of diamond, in the case of the samedischarge power, the higher the discharge voltage is made, the fasterthe speed of synthesis becomes as a general trend (see FIG. 2). In thisway, lengthening the arc column and raising the discharge voltage arevery effective in reducing the electrode consumption of the cathode 1and the anode 2, improving the stability of the discharge, raising thepurity of the synthesized diamond film, improving the quality, andraising the speed of synthesis.

However, if the arc column 5 is made too long, the arc easily disappearsand so there were limits to the conventional method of using a DC arcdischarge. That is, there were the problems that the electrode materialsof the cathode 1 and the anode 2 easily were mixed in the diamond film 8as impurities or that the discharge was unstable and there wasinsufficient reproducibility. Further, the angle of spread of the plasmajet was narrow and only a small area of synthesis was possible. In thisway, it was difficult with the conventional process to stably synthesizea high quality diamond film 8 over a large area.

SUMMARY OF THE INVENTION

Accordingly, the object of the present invention is to solve the aboveproblems in the prior art and provide a process and apparatus forproducing diamond which enables a high purity and high quality diamondfilm to be stably produced at a high speed, over a large area, and withgood reproducibility.

According to a first aspect of the present invention, there is providedan apparatus for producing diamond having a columnar cathode which canbe moved along a common axis, a tubular main anode which is providedconcentrically with said cathode set apart with a clearance therewithand with a front end serving as a plasma jetting port, a tubular pilotanode which is provided concentrically with said cathode and main anodein the clearance between said cathode and said main anode set apart witha clearance therewith and able to be moved along said common axis, apilot gas introduction port which introduces pilot gas to the clearancebetween said cathode and said pilot anode, a main gas introduction portwhich introduces main gas to the clearance between said main anode andsaid pilot anode, a main power supply which connects said main anode andsaid cathode, an auxiliary power source which is connected between saidcathode and said pilot anode, and a substrate holder which is providedat a position facing said jetting port and holds a substrate on which adiamond film is to be formed.

The apparatus preferably has a gas introduction nozzle which is providedin proximity to the plasma jetting port of said main anode and mixes gaswith plasma jetted from said jetting port. Further, the diamondproducing apparatus preferably has a pressure reducible chamber in whichsaid cathode, said main anode, and said pilot anode are housed andfurther a gas introduction port for introducing gas in said chamber isprovided in a wall of said chamber.

According to a second aspect of the present invention, there is provideda process for producing diamond comprised of bringing both a columnarcathode and a tubular pilot anode, provided concentrically around saidcathode set apart with a clearance with said cathode, into proximity toa plasma jetting port of a front end portion of a tubular main anode,provided concentrically around said pilot anode set apart with aclearance with said pilot anode, applying voltage across said cathodeand said pilot anode to convert to plasma a pilot gas introduced in theclearance between said cathode and said pilot anode, then moving thecathod which is near said pilot anode away from said pilot anode along acommon axis, holding the discharge voltage between said cathode and saidpilot anode at a predetermined voltage, then applying voltage acrosssaid cathode and said main anode to convert to plasma a main gasintroduced to the clearance between said main anode and said pilotanode, then moving the pilot anode which is close to the main anode awayfrom the main anode along said common axis while holding the dischargevoltage between said cathode and said pilot anode as it is, holding thedischarge voltage between said cathode and said main anode at apredetermined voltage, and jetting plasma from said jetting port in thestate when holding a main arc generated between said main anode and saidcathod.

In the above process, said pilot gas is preferably argon gas or anotherinert gas and said main gas is preferably a mixed gas of hydrogen gas oran inert gas and a gas comprised of a carbon compound. Further, it ispossible to introduce a gas including the carbon compound gas into theplasma Jetted from the plasma jetting port of said main anode so as tosuitably produce the desired diamond. Note that as the pilot gas, use ispreferably made of argon gas or another inert gas, said main gas ispreferably hydrogen gas or an inert gas. Further, a desired diamond maysuitably be produced by producing diamond according to the presentinvention in a chamber reduced in pressure and introducing atmosphericgas into said chamber from a gas introduction port provided in a wall ofsaid chamber. In preferable aspect of the present invention, it ispossible to produce diamond from a pilot gas which is argon gas oranother inert gas, a main gas which is hydrogen gas or an inert gas, andatmospheric gas which is a gas comprised of a carbon compound. Further,according to the present invention, there is provided a process forproducing diamond wherein the pilot gas is argon gas or another inertgas, said main gas is hydrogen gas or an inert gas, and said atmosphericgas is a mixed gas comprised of a gas comprised of a carbon compound, anoxidizing gas, halogen gas, or halogenated hydrogen gas.

According to a third aspect of the present invention, there is provideda process for gas phase synthesis of diamond by a DC plasma jet whereina plasma jet produced by DC arc discharge using a DC plasma torch ismade to strike a substrate to grow diamond on the substrate, saiddiamond gas phase synthesis process having a plurality of plasma torchanodes arranged coaxially in a telescoped structure.

In the third aspect, preferably part or all of the electrodes of saidplasma torch are of a construction enabling movement in the axialdirection of the torch and the electrodes are made to move and thedischarge voltage changed during the generation of the plasma jet.Further, according to a preferred aspect of the present invention, adesired diamond can be produced by gas phase synthesis by applying amagnetic field in the axial direction of said plasma torch and causing aLorentz force to act on the arc column to forcibly cause the anode pointto rotate.

According to a fourth aspect of the present invention, there is providedan apparatus for gas phase synthesis of diamond by the DC plasma jetdiamond gas phase synthesis process wherein a non-transfer type plasmatorch which generates a plasma jet by DC arc discharge, a substrateholder, and a movement mechanism which enables the positions of theplasma torch and substrate holder to be changed are disposed in areduced pressure chamber to which a vacuum pump is connected, saidapparatus for gas phase synthesis of diamond having a plurality ofanodes of the plasma torch arranged coaxially in a telescoped structure.

In the fourth aspect of the present invention, part or all of theelectrodes of the plasma torch are able to move in the axial directionof the torch during generation of the plasma jet, one or a plurality ofnozzles for blowing gas to the plasma jet generated from the plasmatorch may be provided at the outside of the main anode and a gas supplysystem for supplying gas to the nozzles may be connected to the nozzles,and there may be a permanent magnet or electromagnet for applying amagnetic field in the axial direction of the plasma torch and causing aLorentz force to act on the arc column so as to forcibly rotate theanode point.

According to a fifth aspect of the present invention, there is provideda process for gas phase synthesis of diamond using a DC plasma jet whichcauses a plasma jet generated by DC arc discharge using a DC plasmatorch to strike a substrate to cause growth of diamond on the substrate,said process for gas phase synthesis of diamond comprised by applying amagnetic field to the arc from a direction orthogonal to the axialdirection of the torch so as to cause deflection of the plasma jet so asto broaden the area of irradiation of the plasma jet and enable anincrease in the area of synthesis of the diamond and by having aplurality of anodes of the plasma torch arranged coaxially in atelescoped structure.

According to a sixth aspect of the present invention, there is provideda process for gas phase synthesis of diamond, using a DC plasma jetwhich causes a plasma jet generated by DC arc discharge using a DCplasma torch to strike a substrate to cause growth of diamond on thesubstrate, said process for gas phase synthesis of diamond comprised byapplying a magnetic field to the plasma jet from a direction orthogonalto the axial direction of the torch so as to cause deflection of theplasma jet so as to broaden the area of irradiation of the plasma jetand enable an increase in the area of synthesis of the diamond and byhaving a plurality of anodes of the plasma torch arranged coaxially in atelescoped structure.

In the fifth and sixth aspects, preferably a magnetic field is appliedto the plasma jet from a direction orthogonal to the axial direction ofthe torch so as to cause deflection of the plasma Jet and therebybroaden the area of irradiation of the plasma jet and increase the areaof synthesis of the diamond. A preferable method of application of thedeflecting magnetic field is to apply a magnetic field from mutuallyorthogonal X and Y two directions in a plane orthogonal to the axialdirection of the torch so as to enable the direction of the combinedmagnetic field to be freely changed within said plane, whereby thedirection of the deflection of the plasma jet can be changedtwo-dimensionally within the plane.

According to a seventh embodiment of the present invention, there isprovided an apparatus for synthesis of diamond by the DC plasma jetdiamond gas phase synthesis process wherein a non-transfer type plasmatorch which generates a plasma jet by DC arc discharge, a substrateholder, and a movement mechanism which enables the positions of theplasma torch and substrate holder to be changed are disposed in areduced pressure chamber to which a vacuum pump is connected, saidapparatus for gas phase synthesis of diamond having connected to it anelectromagnet, and a control device for the same, able to apply amagnetic field to the arc from between the cathode and anode in adirection orthogonal to the axial direction of the torch, and having aplurality of anodes of the plasma torch arranged coaxially in atelescoped structure.

According to an eighth embodiment of the present invention, there isprovided an apparatus for synthesis of diamond by the DC plasma jet CVDprocess wherein a non-transfer type plasma torch which generates aplasma jet by DC arc discharge, a substrate holder, and a movementmechanism which enables the positions of the plasma torch and substrateholder to be changed are disposed in a reduced pressure chamber to whicha vacuum pump is connected, said apparatus for gas phase synthesis ofdiamond having connected to it an electromagnet, and a control devicefor the same, able to apply a magnetic field to the plasma jet fromoutside the anodes in a direction orthogonal to the axial direction ofthe torch, and having a plurality of anodes of the plasma torch arrangedcoaxially in a telescoped structure.

In the seventh and eighth aspects of the present invention, theelectromagnet is preferably comprised of two systems of electromagnetsable to apply a magnetic field from the mutually orthogonal X and Y twodirections in a plane orthogonal to the axial direction of the torch.

According to a ninth embodiment of the present invention, there isprovided a process for gas phase synthesis of diamond by a DC plasma jetwherein a plasma jet generated by DC arc discharge using a DC plasmatorch is made to strike a substrate to cause growth of diamond on thesubstrate, said process for gas phase synthesis of diamond having aplurality of anodes of the plasma torch arranged coaxially in atelescoped structure and having the relative positions of the electrodesbeing able to be changed so as to enable a change of the dischargeposition of the plasma and stabilization of the discharge.

In this aspect, preferably the cathode serving as the dischargeelectrode for generating the plasma jet is made variable, the cathode ismade to rotate about the axial line of the torch so as to make thedischarge position variable, the cathode is made to vibrate at anydesired oscillation frequency so as to make the discharge positionvariable, the anode serving as the discharge electrode for generatingthe plasma jet is made variable, the anode is made to rotate about theaxial line of the torch so as to make the discharge position variable,or the anode is made to vibrate at any desired oscillation frequency soas to make the discharge position variable.

According to a tenth aspect of the present invention, there is providedan apparatus for synthesis of diamond by the DC plasma jet CVD processwherein a non-transfer type plasma torch which generates a plasma jet byDC arc discharge, a substrate holder, and a movement mechanism whichenables the positions of the plasma torch and substrate holder to bechanged are disposed in a reduced pressure chamber to which a vacuumpump is connected, said apparatus for synthesis of diamond beingprovided with an anode electrode and cathode electrode for arc dischargeand an electrode drive means for changing the relative positions of thedischarge electrodes and having a plurality of anodes of the plasmatorch arranged coaxially in a telescoped structure.

In this aspect, preferably said electrode drive means drives the cathodeand causes rotation about the axial line of the torch so as to make thedischarge position variable, said electrode drive means drives the anodeand causes rotation about the axial line of the torch so as to make thedischarge position variable, or said drive means is a motor.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from the descriptionset-forth below with reference to the accompanying drawings, wherein:

FIG. 1 is a detailed structural view of a plasma torch of a diamondproducing apparatus according to the prior art;

FIG. 2 is a graph showing the relationship between the discharge voltageand film-forming speed in gas phase synthesis of diamond;

FIG. 3 is a structural view showing the principle of a producingapparatus of a third aspect of the present invention;

FIG. 4 is a structural view showing the principle of a diamond producingapparatus according to a fifth aspect of the present invention;

FIG. 5 is a structural view of a diamond producing apparatus accordingto Example 1 of the present invention;

FIG. 6 is a detailed structural view of a plasma torch of a diamondproducing apparatus according to Example 1 of the present invention;

FIGS. 7(a) and 7(b) are side views (part 1) of a plasma torch forexplaining the process for producing diamond according to Example 4 ofthe present invention;

FIG. 8 is a side view (part 2) of a plasma torch for explaining theprocess for producing diamond according to Example 4 of the presentinvention;

FIG. 9 is a structural view of a diamond producing apparatus accordingto Example 2 of the present invention;

FIG. 10 is a structural view of a diamond producing apparatus accordingto Example 3 of the present invention;

FIGS. 11(a) and 11(b) are side views of a plasma torch for explainingComparative Example 2 for the diamond producing apparatus according tothe present invention;

FIG. 12 is a structural view of a diamond producing apparatus accordingto Example 8 of the present invention;

FIG. 13 is a structural view of a diamond producing apparatus accordingto Example 8 of the present invention;

FIG. 14 is a structural view of a diamond producing apparatus accordingto Example 11 of the present invention;

FIG. 15 is a structural view of a diamond producing apparatus accordingto Example 11 of the present invention;

FIG. 16 is a structural view of a diamond producing apparatus accordingto Example 12 of the present invention;

FIG. 17 is a schematic view of a diamond producing apparatus accordingto Example 12 of the present invention;

FIG. 18 is a graph showing the distribution of thickness of a diamondfilm synthesized in Example 12 of the present invention;

FIG. 19 is a schematic view of a diamond producing apparatus accordingto Example 13 of the present invention;

FIG. 20 is a schematic view of a diamond producing apparatus accordingto Example 13 of the present invention;

FIG. 21 is a graph showing the distribution of thickness of the diamondfilm synthesized in Example 13 of the present invention;

FIG. 22 is a schematic view of a diamond producing apparatus accordingto Example 14 of the present invention;

FIG. 23 is a graph showing the changes over time of the dischargevoltage in Example 14 of the present invention;

FIG. 24 is a schematic view of a diamond producing apparatus accordingto Example 15 of the present invention; and

FIG. 25 is a graph showing the changes over time of the dischargevoltage in Example 15 of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the diamond producing apparatus according to the first aspect of thepresent invention, the construction is such that a tubular pilot anodeis interposed concentrically in the clearance between a columnar cathodeand a tubular main anode, provided concentrically with the cathode setapart with a clearance from the same, set apart with a clearance fromthe columnar cathode and the tubular anode and that the cathode andanode can be moved along a common axis. Further, an auxiliary powersource is connected between the cathode and pilot anode, a main powersource is connected between the main anode and cathode, and there are apilot gas introduction port for introducing pilot gas in the clearancebetween the cathode and the pilot anode and a main gas introduction portfor introducing main gas in the clearance between the main anode and thepilot anode.

Therefore, with the process for producing diamond in accordance with thesecond aspect of the present invention, it is possible to synthesizediamond by bringing both the cathode and pilot anode into proximity withthe plasma jetting port, that is, the front end portion of the mainanode, applying voltage across said cathode and said pilot anode toconvert to plasma a pilot gas introduced in the clearance between saidcathode and said pilot anode, then moving the cathode which is near saidpilot anode away from said pilot anode along a common axis, holding thevoltage between said cathode and said pilot anode at a predeterminedvoltage, then applying voltage across said cathode and said main anodeto convert to plasma a main gas introduced to the clearance between saidmain anode and said pilot anode, then moving the pilot anode which isclose to the main anode away from the main anode along said common axis,holding the discharge voltage between said cathode and said main anodeat a predetermined voltage, and jetting plasma from said jetted port inthe state when holding a main arc generated between said main anode andsaid cathod.

By this, using the pilot arc generated in the clearance between thecathode and the pilot anode, it is possible to control the dischargevoltage between the cathode and main anode while preventingextinguishment of the main arc generated in the clearance between thecathode and the main anode. In particular, by reducing the electrodedistance between the cathode and the main anode when igniting the mainarc and increasing the electrode distance between the cathode and mainanode after the main arc is generated, it is possible to make thedischarge voltage between the cathode and the main anode much highercompared with the prior art. Due to this, it possible to stably producea high purity and high quality diamond film at a high speed and with agood reproducibility.

Further, as the pilot gas, argon (Ar) gas, which gives a stabledischarge, is most suitable, but helium (He) gas and other inert gasesor hydrogen (H₂) gas may also be included. Further, the main gas ispreferably mainly H₂ gas, which has a high discharge voltage and playsan important role in the gas phase synthesis of diamond, but Ar gas, Hegas, and other inert gases may also be included.

Further, to synthesize the diamond, a gas comprised of carbon compoundsserving as the feedstock of the diamond must be fed in the plasma. Asthe feed method, there are the methods of mixing it with the main gas,blowing it into the plasma from the gas introduction nozzle outside themain anode, or introducing it in the chamber as atmospheric gas. Themethod of feeding it as pilot gas is not preferable since it lowers thestability of the pilot arc.

Further, to improve the quality of the diamond film, oxygen, steam, orother oxidizing gases, halogen gases, halogenated hydrogen gas, etc. mayalso be fed in the plasma. In this case, as the feed method, there arethe methods of mixing it with the main gas, blowing it into the plasmafrom the gas introduction nozzle outside the main anode, or introducingit into the chamber as atmospheric gas. The method of feeding it aspilot gas is not preferable since it lowers the stability of the pilotarc.

In the third aspect of the present invention, in the DC plasma jet CVDprocess, by making the anode of the plasma torch a telescoped structure,the arc can be stabilized and the electrode consumption reduced andfurther by causing generation of plasma with a large angle of spread ofthe plasma jet, it is possible to synthesize high purity and highquality diamond.

Further, in the fourth aspect of the present invention, by applying amagnetic field to the arc column and forcibly causing the anode point torotate, the arc is stabilized and the electrode consumption is reducedand further by causing generation of plasma with a large angle of spreadof the plasma jet, it is possible to synthesize high purity and highquality diamond over a large area.

Regarding the third aspect, in general, with a DC arc discharge, withthe same discharge power, elongating the arc column, raising thedischarge voltage, and lowering the discharge current results in lesselectrode consumption and further a smaller voltage fluctuation rate.Further, in diamond synthesis, in the case of the same discharge power,the higher the discharge voltage is made, the faster the speed ofsynthesis tends to become (see FIG. 2). In this way, elongating the arccolumn and raising the discharge voltage can be expected to have suchmajor effects as reducing the electrode consumption, improving thestability of the discharge voltage, raising the purity and quality ofthe diamond which is synthesized, and raising the speed of synthesis. Ifthe arc is made too long, however, the arc tends to easily disappear (orextinguish), so there are limits to this method.

Further, the plasma jet is ejected from a narrow anode nozzle, so theangle of spread of the plasma jet is small and the area of the filmwhich is formed is small as well. Even if the nozzle diameter is madelarger, there is little effect since the thermal plasma itself acts toreduce the surface area and reduce the diffusion of the heat. Further,if the nozzle diameter is made too large, the arc length becomes longand the arc easily is extinguished.

In the third aspect of the present invention, the above problems areattempted to be resolved by making the anode a telescoped structure.That is,

(1) By providing a plurality of anodes, the arc current is dispersed andthe consumption of the anodes lowered.

(2) Separate roles are assigned to each of the anodes, e.g., providingan anode for maintaining the plasma, a main anode for generating theplasma jet, and an anode for spreading the plasma jet.

(3) Even under conditions where there is no discharge with a singleanode, a plasma jet is continually generated by the other anodes, so thedischarge can be maintained even under such conditions.

(4) Since a number of discharges occur, even with voltage fluctuationswith individual electrodes, the effects are averaged out and becomesmaller.

FIG. 3 shows the principle of the third aspect of the present inventionand shows the synthesis of diamond by a plasma torch having arepresentative three anodes. In the figure, 1 is a cathode, 2a is afirst anode, 2b is a second anode, 2c is a third anode, 4a is a firstpower source, 4b is a second power source, 4c is a third power source, 5is an arc-column, 6 is a plasma jet, 7 is a substrate, 8 is a diamondfilm, 9a is a first gas, 9b is a second gas, 9c is a third gas, 10 is aninsulator, and 11 is a magnet.

In the example of FIG. 3, the first anode 2a closest to the cathode isthe pilot anode for maintaining the discharge. It is low in power andstable in discharge. The second anode 2b is the main anode and generatesa high voltage discharge of an arc of a long length which wouldextinguish with a single anode. The third anode 2c is an electrode forspreading the plasma jet. It has a large nozzle diameter and increasesthe angle of spread of the plasma jet. As the discharge gas, use is madeof Ar, which facilitates a stable discharge, for the first gas 9a, andhydrogen, which plays an important role in the gas phase synthesis ofdiamond, as the second and third gases 9b and 9c. Methane, which servesas the feedstock for the diamond, is introduced along with the hydrogenas the third gas.

As the discharge gas in the method of the present invention, it isnecessary to use hydrogen, which plays an important role in the gasphase synthesis of diamond. Further, Ar, He, and other inert gases arepreferable for obtaining a stable discharge. Since there are a pluralityof anodes, there are also a plurality of discharge gas introductionports, so these gases may be fed alone or mixed together in accordancewith the torch structure or as needed. Preferably, as the first gasclosest to the cathode, use is made of Ar so as to protect the cathodeand stabilize the discharge. For the second gas on, use may be made ofhydrogen with its high discharge voltage.

To synthesize diamond, a carbon compound gas forming the feedstock ofthe diamond must be fed into the plasma jet. As the feed method, it maybe mixed in the discharge gas, blown from a nozzle outside the anodesinto the plasma jet, or fed as atmospheric gas. It may also be fed asthe first gas, but this is not preferable since it lowers the dischargestability or has a detrimental effect on the cathode.

To improve the quality of the diamond film, oxygen, steam, or otheroxidizing gas, a halogen gas, halogenated hydrogen gas, etc. may also befed into the plasma jet. In this case, as the feed method, it may bemixed in the discharge gas, blown from a nozzle outside the anodes intothe plasma jet, or fed as atmospheric gas. It may also be fed as thefirst gas, but this is not preferable since it lowers the dischargestability or has a detrimental effect on the cathode. To control thedischarge voltage, the apparatus is constructed to allow movement of thecathode and the anodes during the discharge. During discharge, theelectrodes may be moved to adjust the discharge voltage to apredetermined level. In particular, when igniting the arc, the distancebetween the electrodes may be made shorter and then when the arc hasbeen generated, the distance between electrodes may be made greater soas to further increase the discharge voltage.

In general, the DC arc discharge is discharged on a line between thecathode point and the anode point. The problem here is that thedischarge current concentrates at the single anode point on the anodeelectrode, so the temperature at that portion becomes extremely high andtherefore the anode material evaporates and ends up mixing in the plasmajet. Further, since the anode point moves irregularly, the dischargevoltage or the shape of the plasma jet end up changing each time and astable discharge cannot he obtained. Due to such a problem, usually theplasma gas is fed between the electrodes as a swirling (or rotating orcirculating) stream to rotate the anode point. With this method,however, a high gas flow is required to stably rotate the anode point,so the discharge conditions end up being limited.

In the fourth aspect of the present invention, by applying a magneticfield in the axial direction of the torch, a Lorentz force is made toact on the arc to forcibly rotate the anode point, thereby giving thefollowing effects:

(1) The rise of temperature of the anode point is prevented and theentry of impurities into the plasma jet due to evaporation of the anodematerial is reduced, so the anode lifetime is prolonged.

(2) By averaging together the arc fluctuations, the fluctuations in thedischarge voltage and the shape of the plasma jet can be suppressed anda stable plasma jet generated.

(3) Since the spread of the arc becomes greater, the spread of theplasma jet also becomes greater.

(4) Even with a small gas flow which cannot be expected to have a swirleffect, it is possible to easily rotate the anode point.

In the view of FIG. 3, reference numeral 11 is a magnet for rotating theanode point.

As the means for generating the magnetic field, there is the method ofusing a permanent magnet and the method of using an electromagnet, butit is sufficient if a magnetic field is applied just near the anodepoint, so use of a permanent magnet is more effective in that it cangenerate a strong magnetic field with a small volume. As a permanentmagnet, a strong magnet of the Nd--Fe--B series or Sm--Co series ispreferable. As to the method of placement, a location as close to theanode point as possible is best. Preferably, it is provided in the anodeelectrode. At this time, it is necessary to take care to prevent a risein temperature of the magnet or generation of rust due to the coolantwater.

FIG. 4 is a conceptual view for explaining a fifth aspect of the presentinvention. In the figure, 1 is a cathode, 2a a first anode, 2b a secondanode, 5 an arc, 6 a plasma jet, 7 a substrate, 8 a diamond film, 9 anintroduced gas, 12 lines of magnetic flux, 13 a yoke, and 14 a coil.

If a magnetic field 12 is applied to the arc 5 in a direction orthogonalto the same, a Lorentz force (vertical direction of paper surface inFIG. 4) is generated in the direction orthogonal to the current (arc)and the magnetic field. This Lorentz force causes the arc to bend in thevertical direction of the paper surface. Along with this, the plasma jetis also bent in that direction. If an alternating current is applied tothe coil 14 for generating the magnetic field, the direction of theforce acting on the arc rises and falls in the vertical direction of thepaper surface and the deflection of the plasma jet 6 oscillates. If thisplasma jet 6 is impinged on the substrate 7 to synthesize a diamond film8, the area of formation of the diamond expands in the lateral direction(vertical direction of the paper surface in FIG. 4).

If a magnetic field is applied from the mutually orthogonal X and Y twodirections, the direction of the Lorentz force can be freely changed inthe XY plane. Therefore, by scanning the direction of deflection of theplasma jet, it is possible to considerably increase the area ofsynthesis of the diamond.

Further, by deflecting the arc, it is possible to move the contact pointbetween the arc and the anode, that is, the anode point. The anode pointbecomes extremely high in temperature, so the electrode materialevaporates and ends up contaminating the plasma jet, but by deflectingthe arc and shortening the time during which the anode point stops at asingle point, the consumption of the electrode material is suppressedand the purity of the plasma jet is increased, which is effective inraising the purity of the diamond.

To raise the effect of the magnetic field deflection according to thepresent invention, it is necessary to increase the diameter of the anodenozzle and lengthen the arc on which the magnetic field acts. If the arcis lengthened, however, the arc easily disappears (easily extinguishes).Therefore, for effective utilization of the present invention, a plasmatorch of a telescoped anode structure enabling the arc length to beincreased is suitable.

The sixth aspect of the present invention causes a magnetic field to acton the plasma jet ejected from the anode. The plasma jet near the anodeis high in temperature and high in degree of electrolytic dissociation.Therefore, it is possible to deflect the plasma jet in the same way asapplying a magnetic field to the arc. Further, it is similarly possibleto apply a magnetic field from the mutually orthogonal X and Y twodirections to change the direction of the Lorentz force in the XY plane.

Compared with the method of applying a magnetic field to the arc as inthe fifth aspect of the present invention, this aspect enables themagnetic circuit to be established outside the anodes, so theconstruction is simpler and there is no need to make the arc lengthlonger or the nozzle diameter larger. The plasma jet, however, is lowerin the charge density compared with the arc, so the effect of deflectionis smaller and no effect appears on movement of the anode point.

EXAMPLES

The present invention will now be further illustrated by, but is by nomeans limited to, the following Examples.

Examples 1 to 3

FIG. 5 is a constitutional view of an apparatus for producing diamondusing a plasma torch according to Example 1 of the present invention,while FIG. 6 is a detailed constitutional view of a plasma torchaccording to Example 1 of the present invention.

In FIG. 5 and FIG. 6, 15 is a chamber for synthesis of diamond underreduced pressure, 16 is a gas introduction port for introducingatmospheric gas from outside the chamber 15 to inside the chamber 15, 17is a port for exhausting the inside of the chamber 15, 18 is substrateholder which carries the substrate 19, 20 is the XY stage, 21 is alinear motor which causes the XY stage 18 to move up and down, and 22 isa gas feed means for feeding various different types of gases requiredfor the formation of a diamond film and which is connected to the gaspiping 23a to 23d. The other ends of the gas piping 23a to 23d areconnected to the pilot gas introduction port 27 in the clearance betweenthe cathode 24 and the pilot anode 25, the main gas introduction port 28in the clearance between the main anode 26 and the pilot anode 25, andthe gas introduction nozzle 29 and the gas introduction port 16 in thechamber 15 wall.

In FIG. 5 and FIG. 6, 24 is a columnar cathode with a pointed front endcomprised of tungsten and/or copper, 30a and 30b are coolant pipingwhich feed and drain coolant like cooling water to the cathode 24, and31 is a cathode movement means which moves the cathode 24 up and down.For example, as shown in FIG. 7(a) and (b), during discharge, thecathode 24 may be moved along a common axis. Reference numeral 25 is atubular pilot anode 25 which is provided concentrically with the cathode24 and main anode 26 between the cathode 24 and main anode 26 and whichassists the maintenance of the discharge state. It has formed in it apilot gas introduction port 27 which introduces pilot gas to theclearance between the cathode 24 and the pilot anode 25. Referencenumerals 32a and 32b are coolant piping which feed cooling water andother coolant to the pilot anode 25 and drain the same, while 33 is apilot anode movement means which moves the pilot anode 25 up and down.As shown in FIG. 7(b) and FIG. 8, during the discharge, the pilot anode25 may be moved along a common axis with the cathode 24.

Reference numeral 26 is a tubular main anode comprised of tungstenand/or copper and provided concentrically near the pilot anode 25. Amain gas introduction port 28 is formed which introduces main gas to theclearance between the main anode 26 and the pilot anode 25. Further, thefront end of the main anode 26 forms a plasma jetting port. Referencenumerals 34a and 34b are coolant piping which feed cooling water orother coolants to the main anode 26 and drain the same. The cathode 24,the pilot anode 25, and the main anode 26 constitute the plasma torch.Reference numeral 29 is a gas introduction nozzle. Reference numeral 35is an auxiliary power source. The pilot gas introduced to the clearancebetween the cathode 24 and the pilot anode 25 is converted to plasma byDC arc discharge. Reference numeral 19 is a main power source which isconnected between the main anode 26 and the cathode 24. The main gaswhich is introduced to the clearance between the main anode 26 and thepilot anode 25 is converted to plasma by the DC arc discharge. Note that19 is a substrate comprised of molybdenum (Mo) on which the diamond filmis formed.

As explained above, according to the apparatus for producing diamond ofExample 1 of the present invention, a pilot anode 25 is interposedconcentrically in the clearance between the cathode 24 and the mainanode 26, an auxiliary power source 35 is connected between the cathode24 and the pilot anode 25, and a main power source 36 is connectedindependent of the auxiliary power source 35 between the cathode 24 andthe main anode 26. Further, the apparatus is constructed so as to enablethe cathode 24 and the pilot anode 25 to be moved along a common axisduring discharge.

Therefore, first, the cathode 24 and the pilot anode 25 are brought intoproximity to the jetting port of the main anode 26, voltage is appliedacross the cathode 24 and the pilot anode 25 so as to convert to plasmathe pilot gas introduced to the clearance between the cathode 24 and thepilot anode 25, then the cathode 24 in proximity to the pilot anode 25is moved away from the pilot anode 25 along the common axis to hold thedischarge voltage between the cathode 24 and the pilot anode 25 at apredetermined voltage, then, voltage is applied across the cathode 24and the main anode 26 so as to convert to plasma the main gas introducedto the clearance between the pilot anode 25 and the main anode 26, thenwhile holding the discharge voltage between the cathode 24 and the pilotanode 25, the pilot anode 25 in proximity to the main anode 26 is movedaway from the main anode 26 along the common axis so as to hold thedischarge voltage between the cathode 24 and the main anode 26 to apredetermined voltage, whereby it is possible to jetting plasma tosynthesize diamond in the state with the main arc 5 generated heldconstant.

As seen above, using the pilot arc generated in the clearance betweenthe cathode 24 and the cathode 24, it is possible to preventextinguishment of the main arc generated between the cathode 24 and themain anode 26 and control the discharge voltage between the cathode 24and the main anode 26. In particular, by reducing the electrode distancebetween the cathode 24 and the main anode 26 when igniting the main arcand increasing the electrode distance between the cathode 24 and themain anode 26 after the main arc has been generated, it is possible toraise the discharge voltage between the cathode 24 and the main anode 26much more than in the past in the state while holding the main arc 5.Due to this, it is possible to stably produce a high purity and highquality diamond film at a high speed and with a good reproducibility.

Note that in Example 1, as the location for introduction of the carboncompound gas, it is possible to use the main gas introduction port 28 atthe clearance between the main anode 16 and the pilot anode 25, the gasintroduction nozzle 29 placed near the jetting port of the plasma jet ofthe main anode 26, or the gas introduction port 16 formed in the chamber15 wall. At this time, as with the diamond producing apparatus accordingto Example 2 shown in FIG. 9, it is possible to use the gas introductionnozzle 29 near the plasma jetting port of the main anode 26, or, as withthe diamond producing apparatus according to Example 3 shown in FIG. 10,it is possible to introduce it from the gas introduction port 16 of thechamber 15 wall to the inside of the chamber 15. These may be usedindependently or may be used combined in any way. However, use of thepilot gas introduction port 27 at the clearance between the cathode 24and the pilot anode 25 is not preferable from the viewpoint of thestability of the pilot arc.

Example 4

Next, an explanation will be made of a process for producing diamond ofExample 4 of the present invention, wherein use is made of the diamondproducing apparatus of Example 1 shown in FIG. 6, argon gas isintroduced from the pilot gas introduction port 27, and a mixed gas ofthe methane gas (the feedstock gas), and hydrogen gas is introduced fromthe main gas introduction port 28, referring to FIG. 5, FIG. 6, FIG.7(a) and (b), and FIG. 8.

First, the cathode 24 and the pilot anode 25 are set at the positionsclosest to the plasma jetting port of the main anode 26 (FIG. 7(a)) anda substrate 19 comprised of an Mo substrate of 50×50×5 mm size is set ona water-cooled substrate holder 18. Next, the inside of the chamber 15is exhausted to lower the pressure to under 0.01 Torr, then 20liters/minute of Ar gas is introduced to the clearance between thecathode 24 and the pilot anode 25 from the pilot gas introduction port27 and 50 liters/minute of hydrogen gas and 1 liter/minute of methanegas are introduced to the clearance between the main anode 26 and thepilot anode 25 from the main gas introduction port 28.

Next, voltage is applied between the cathode and the pilot anode fromthe auxiliary power source 35 to cause generation of a pilot arc with apilot current of 20A. The cathode 24 is moved away from the pilot anode25 while maintaining the discharge state to make the pilot voltage 50 V(FIG. 7(b)). Next, voltage is applied between the cathode and the mainanode from the main power source 36 to generate the main arc at a mainarc current of 40A. The cathode 24 and the pilot anode 25 are slowlymoved away from the main anode 26 while maintaining the dischargevoltage to make the main arc voltage 200 V (FIG. 8). At this time, theoverall discharge power is 9 kW.

Next, the pressure inside the chamber 15 is made 50 Torr and the XYstage 18 is brought close to the plasma torch so as to make the surfacetemperature of the substrate 19 raised by the plasma jet 1050° C. Next,by holding these conditions for one hour, a diamond film 37 is formed onthe substrate 19. Note that to study the effects of Example 4 of thepresent invention, the changes in the arc voltage during formation ofthe diamond film 37 and the changes in the temperature of the substrate19 were measured.

Further, the thus synthesized diamond was examined by a scanning typeelectron microscope (SEM) and the types of impurities and theconcentration of the same were investigated by secondary ion massspectrometry (SIMS). The results showed that the change in the main arcvoltage was less than 2 percent and the change in the temperature of thesubstrate 19 was less than ±10° C. Further, the thickness of thesynthesized diamond film 37 was 300 μm and the film-formation speed was300 μm/hour. Further, the position from the center where the thicknessof the diamond film 37 became 80 percent (240 μm) of that of the centerportion was about 15 mm. Also, the results of the analysis of theimpurities by SIMS showed that the concentrations of tungsten and/orcopper, which are the electrode materials of the cathode 24 and the mainanode 26, were under 0.1 ppm.

As explained above, according to the process of production of diamond ofExample 4 of the present invention, first the cathode 24 and the pilotanode 25 are brought into close proximity to the plasma jetting port ofthe main anode 26 (FIG. 7(a)), a voltage is applied across the cathode24 and the pilot anode 25 to convert to plasma the Ar gas introduced tothe clearance between the cathode 24 and the pilot anode 25, then, whilemaintaining the discharge state, the cathode 24 in proximity to thepilot anode 25 is moved away from the pilot anode 25 (see FIG. 7(b)) tohold the discharge voltage between the cathode 24 and the pilot anode 25at a predetermined voltage, then voltage is applied the cathode 24 andthe main anode 26 so as to convert to plasma the main gas introduced tothe clearance between the pilot anode 25 and the main anode 26, then,while maintaining the discharge state, the pilot anode 25 in proximityto the main anode 26 is (or the cathode 24 and the pilot anode 25 are)moved away from the main anode 26 to maintain the discharge voltagebetween the cathode 24 and the main anode 26 to a predetermined voltage,and plasma is jetted to synthesize diamond in a state while maintainingthe main arc (FIG. 8).

By this, it is possible to use the pilot anode generated in theclearance between the cathode 24 and the pilot anode 25 to preventextinguishment of the main arc between the cathode 24 and the main anode26 and control the discharge voltage between the cathode 24 and the mainanode 26. In particular, by reducing the electrode distance between thecathode 24 and the main anode 26 when igniting the main arc andincreasing the electrode distance after the main arc has been generated,it is possible to raise the discharge voltage between the cathode 24 andthe main anode 26 much more than in the past. Due to this, it ispossible to stably produce a high purity and high quality diamond film37 at a high speed and with a good reproducibility.

Note that as the pilot gas, use is made here of Ar gas, which gives astable discharge, but the gas may also include He gas or other inertgases or hydrogen gas. Further, as the main gas, a gas mostly comprisedof hydrogen gas, which plays an important role in the gas phasesynthesis of diamond, is preferable, but Ar gas, He gas, or other inertgases may also be included. Further, as the method of feeding themethane gas serving as the feedstock of the diamond, the gas is mixed inthe main gas introduced from the main gas introduction port 28 betweenthe pilot anode 25 and the main anode 26, but it is also possible to usethe method of blowing it into the plasma jet from the gas introductionnozzle 29 outside the main anode, as in the diamond producing apparatusaccording to Example 2 shown in FIG. 9, or feeding it as atmospheric gasfrom the gas introduction port 16, as in the diamond producing apparatusaccording to Example 3 shown in FIG. 10. However, the method of feedingit as pilot gas from the pilot gas introduction port 27 is notpreferable since this reduces the stability of the pilot arc.

Example 5

Next, an explanation will be made of a process for producing diamond ofExample 5 of the present invention, wherein use is made of the diamondproducing apparatus of Example 2 shown in FIG. 9, methane gas isintroduced as the feedstock gas from the gas introduction nozzle 29, Argas is introduced from the pilot gas introduction port 27, and hydrogengas is introduced from the main gas introduction port 28, referring toFIG. 5, FIG. 7(a) and (b), FIG. 8, and FIG. 9.

First, the cathode 24 and the pilot anode 25 are set at the positionsclosest to the plasma discharge port of the main anode 26 (see FIG.7(a)) and a substrate 19 comprised of an Mo substrate of 50×50×5 mm sizeis set on the substrate holder 18. Next, the inside of the chamber 15 isexhausted from an exhaust port 17 to lower the pressure to under 0.01Torr, then 20 liters/minute of Ar gas is introduced to the clearancebetween the cathode 24 and the pilot anode 25 from the pilot gasintroduction port 27 as the pilot gas and 50 liters/minute of hydrogengas is introduced to the clearance between the main anode 26 and thepilot anode 25 from the main gas introduction port 28 as the main gas.

Next, a pilot arc is caused to be generated at a pilot current of 20A,the cathode 24 is slowly moved away from the pilot anode 25 whilemaintaining the pilot arc, the pilot voltage is raised to 50 V, and thedischarge voltage is held (see FIG. 7(b)). Next, voltage is appliedacross the cathode 24 and the main anode 26 to generate the main arc ata main arc current of 40A, the pilot anode voltage is held at 50 V, andthe pilot anode 25 is slowly moved away from the main anode 26, thevoltage is raised to 200 V, then that discharge voltage is held (seeFIG. 8). At this time, the overall discharge power is 9 kW.

Next, 2 liters/minute of methane gas is introduced as feedstock gas fromthe gas introduction nozzle 29 into the plasma jet 6 and mixed therewith(FIG. 9). By this, the methane gas is also converted to plasma. Next,the pressure inside the chamber 15 is made 50 Torr and the substrate 19is brought close to the plasma torch to make the surface temperature ofthe substrate 1050° C.

Next, these conditions are held for one hour to form a diamond film 37on the substrate 19 and the changes in the arc voltage and the changesin the substrate temperature are measured. Further, the synthesizeddiamond was examined by a scanning type electron microscope (SEM) andthe concentration of impurities was examined by secondary ion massspectrometry (SIMS). As a result, the change in the main arc voltage wasless than 2 percent and the change in the temperature of the substrate19 was less than ±10° C. The thickness of the synthesized diamond film37 was 350 μm and the film-formation speed was 350 μm/hour. Further, theposition from the center where the thickness of the synthesized diamondfilm 37 became 80 percent (280 μm) of that of the center portion wasabout 15 mm. Also, the results of the analysis of the impurities by SIMSshowed that the concentrations of tungsten and/or copper, which are theelectrode materials, were under 0.1 ppm.

As explained above, according to the process of production of diamond ofExample 5 of the present invention, methane gas is introduced asfeedstock gas from the gas introduction nozzle 29 outside of the mainanode 26 into the plasma jet from the plasma torch and mixed with thesame. By this as well, like with Example 4, it is possible to raise thedischarge voltage between the cathode 24 and the main anode 26 much morethan in the past while maintaining the main arc and it is possible tostably produce a high purity and high quality diamond film 37 at a highspeed and with a good reproducibility.

Example 6

Next, an explanation will be made of a process for producing diamond ofExample 6 of the present invention, wherein use is made of the diamondproducing apparatus of Example 3 shown in FIG. 5 and FIG. 10, methanegas is introduced as the feedstock gas from the gas introduction port 16in the chamber 15 wall, argon gas is introduced from the pilot gasintroduction port 27, and hydrogen gas is introduced from the main gasintroduction port 28, referring to FIG. 5, FIG. 7(a) and (b), FIG. 8,and FIG. 10.

First, the cathode 24 and the pilot anode 25 are set at the positionsclosest to the plasma jetting port of the main anode 26 (see FIG. 7(a))and a substrate 19 comprised of an Mo substrate of 50×50×5 mm size isset on the substrate holder 18.

Next, the inside of the chamber 15 is exhausted to lower the pressure tounder 0.01 Torr, then 20 liters/minute of Ar gas is introduced to theclearance between the cathode 24 and the pilot anode 25 from the pilotgas introduction port 27 as the pilot gas and 50 liters/minute ofhydrogen gas is introduced to the clearance between the main anode 26and the pilot anode 25 from the main gas introduction port 28 as themain gas. Next, voltage is applied between the cathode 24 and the pilotanode 25 to generate a pilot arc at a pilot current of 20A, the cathode24 is slowly moved away from the pilot anode 25 while maintaining thepilot arc, and the pilot voltage is raised to 50 V (see FIG. 7(b)).

Next, voltage is applied across the cathode 24 and the main anode 26 togenerate the main arc at a main arc current of 40A, the cathode 24 andthe pilot anode 25 are slowly moved away from the main anode 26 whilemaintaining the main arc, and the main arc voltage is made 200 V (seeFIG. 8). At this time, the overall discharge power becomes 9 kW. In thiscase, the cathode 24 and the pilot anode 25 are moved away from the mainanode 26; the point is to control the distances between the electrode24, 25 and 26 by the electrode movement mechanism 40 in FIG. 12. So, itis needles to say that the main anode 26 may be moved away from pilotanode 25 or the cathode 24. Next, 2 liters/minute of methane gas isintroduced from the gas introduction port 16 in FIG. 10 into the chamber15. By this, the methane gas is mixed in the discharged plasma jet 6,converted to plasma, and fed to the substrate 19.

Next, the pressure inside the chamber 15 is made 100 Torr and thesubstrate 19 is brought close to the plasma torch to make the surfacetemperature of the substrate 1050° C. Next, these conditions are heldfor one hour to form a diamond film 37 on the substrate 19 and thechanges in the arc voltage and the changes in the substrate temperatureare measured.

Further, the synthesized diamond was examined by a scanning typeelectron microscope (SEM) and the concentration of impurities wasexamined by secondary ion mass spectrometry (SIMS).

According to the results of the examination, the change in the main arcvoltage was less than 2 percent and the change in the temperature of thesubstrate 19 was less than ±10° C. The thickness of the synthesizeddiamond film 37 was 300 μm and the film-formation speed was 300 μm/hour.Further, the position from the center where the thickness of thesynthesized diamond film 37 became 80 percent (240 μm) of that of thecenter portion was about 15 mm. Also, the results of the analysis of theimpurities by SIMS showed that the concentrations of tungsten andcopper, which are the electrode materials, were under 0.1 ppm.

As explained above, according to the process of production of diamond ofExample 6 of the present invention, methane gas is introduced asfeedstock gas from the gas introduction port 16 of the chamber 15 wallinto the chamber 15 and converted to plasma. By this as well, like withExample 4, it is possible to raise the discharge voltage between thecathode 24 and the main anode 26 much more than in the past whilemaintaining the main arc and it is possible to stably produce a highpurity and high quality diamond film 37 at a high speed and with a goodreproducibility.

Example 7

Next, an explanation will be made of a process for producing diamond ofExample 7 of the present invention, wherein use is made of the diamondproducing apparatus of Example 3 shown in FIG. 5 and FIG. 10, methanegas and oxygen gas are introduced from the gas introduction port 16 inthe chamber 15 wall, argon gas is introduced from the pilot gasintroduction port 27, and hydrogen gas is introduced from the main gasintroduction port 28, referring to FIG. 5, FIG. 7(a) and (b), FIG. 8,and FIG. 10.

First, the cathode 24 and the pilot anode 25 are set at the positionsclosest to the plasma jetting port of the main anode 26 (see FIG. 7(a))and a substrate 19 comprised of an Mo substrate of 50×50×5 mm size isset on the substrate holder 19. Next, the inside of the chamber 15 isexhausted to lower the pressure to under 0.01 Torr, then 20liters/minute of Ar gas is introduced from the pilot gas introductionport 27 as the pilot gas and 50 liters/minute of hydrogen gas isintroduced from the main gas introduction port 28 as the main gas intothe pilot gas introduction port 27 of the plasma torch and the main gasintroduction port 28, respectively.

Next, a pilot arc is generated at a pilot current of 20A, the cathode 24is slowly moved away from the pilot anode 25 while maintaining the pilotarc, and the pilot voltage is raised to 50 V (see FIG. 7(b)). Next, themain arc is generated at a main arc current of 40A, then the cathode 24and the pilot anode 25 are slowly moved away from the main anode 26while maintaining the main arc, and the main arc voltage is made 200 V(see FIG. 8). At this time, the overall discharge power becomes 9 kW. InFIG. 8 the distance between the cathode 24 and the pilot anode 25 ismaintained nearly equal to that of FIG. 7(b), on the other hand thedistance between the pilot anode 25 and the main anode 26 is increasedthan that of FIG. 7(b).

Next, a mixed gas comprising 3 liters/minute of methane gas and 0.5liter/minute of oxygen gas is introduced from the gas introduction port16 into the chamber 15. By this, the methane gas and oxygen gas aremixed in the plasma jet 6, converted to plasma. Next, the pressureinside the chamber 15 is made 50 Torr and the substrate 19 is broughtclose to the plasma torch to make the surface temperature of thesubstrate 1050° C.

Next, these conditions are held for one hour to form a diamond film 37.At this time, the changes in the arc voltage and the changes in thesubstrate temperature during the synthesis of the diamond film 37 weremeasured. Further, the synthesized diamond was examined by a scanningtype electron microscope (SEM) and the concentration of impurities wasexamined by secondary ion mass spectrometry (SIMS).

According to the results, the change in the main arc voltage was lessthan 2 percent and the change in the temperature of the substrate 19 wasless than ±10° C. The thickness of the synthesized diamond film 37 was300 μm and the film-formation speed was 300 μm/hour. Further, theposition from the center where the thickness of the synthesized diamondfilm 37 became 80 percent (240 μm) of that of the center portion wasabout 20 mm. Also, the results of the analysis of the impurities by SIMSshowed that the concentrations of tungsten and/or copper, which are theelectrode materials, were under 0.1 ppm.

As explained above, according to the process of production of diamond ofExample 7 of the present invention, a mixed gas of methane gas as thefeedstock gas and oxygen gas as the oxidizing gas is introduced from thegas introduction port 16 of the chamber 15 wall into the chamber 15 andconverted to plasma. However, the addition of the oxidizing gas enablesthe quality of the diamond film 37 to be further improved. By this, likewith Example 4, it is possible to raise the discharge voltage betweenthe cathode 24 and the main anode 26 much more than in the past whilemaintaining the main arc and it is possible to stably produce a highpurity and high quality diamond film 37 at a high speed and with a goodreproducibility.

Note that in Example 7, use was made of oxygen gas as the oxidizing gas,but it is also possible to use steam or other oxidizing gases, halogengas, halogenated hydrogen gas, etc. instead of oxygen gas.

Comparative Example 1

Next, an explanation will be given of the process for producing diamondusing a diamond producing apparatus of the prior art shown in FIG. 1while referring to FIG. 1.

First, a substrate 7 comprised of an Mo substrate of 50×50×5 mm is heldon an XY stage. Next, the inside of the chamber is exhausted to reducethe pressure to under 0.01 Torr, then 20 liters/minute of Ar gas, 50liters/minute of hydrogen gas, and 1 liter/minute of methane gas areintroduced as plasma gas to the clearance between the columnar cathode 1with the sharp front end and the tubular anode 2 provided concentricallynear the cathode 1.

Next, the pressure inside the chamber is held at 50 Torr and an arcgenerated with an arc current of 90A and an arc voltage of 100 V, thenthe XY stage is brought close to the plasma torch to make the surfacetemperature of the substrate 1050° C.

Next, these conditions are held for one hour to synthesize the diamondfilm 8 and the changes in the arc voltage and the changes in thetemperature of the substrate on which the film is formed were measured.Further, the synthesized diamond was examined by a scanning typeelectron microscope (SEM) and the concentration of impurities wasexamined by secondary ion mass spectrometry (SIMS).

The results showed that the change in the arc voltage was about 5percent and the change in the temperature of the substrate 7 was ±30° C.Further, the thickness of the synthesized diamond film 8 was 200 μm andthe film-formation speed was 200 μm/hour. Further, the position from thecenter where the thickness of the synthesized diamond film 8 became 80percent (160 μm) of that of the center portion was about 10 mm. Also,the results of the analysis of the impurities by SIMS showed that theconcentrations of tungsten and/or copper, which are the electrodematerials, were several ppm.

As explained above, according to the Comparative Example 1, thefilm-forming speed is slower compared with all of the examples and theuniformity of the thickness of the diamond film 8 synthesized in thesubstrate was inferior.

Comparative Example 2

An explanation will be made of the process for production of diamondaccording to Comparative Example 2, where use is made of the improveddiamond producing apparatus of the prior art shown in FIG. 11 and thecathode is moved to adjust the discharge voltage, referring to FIG. 11.The difference from Comparative Example 1 is that it is possible to movethe cathode 1 along a common axis. Further, the arc current is made alow 40A and the discharge voltage is raised to 200 V.

First, the columnar cathode 1 with the sharp front end is set to theposition closest to the plasma discharge port of the tubular anode 2provided concentrically near the cathode 1 and a substrate comprised ofMo of 50×50×5 mm size is placed on the XY stage.

Next, the inside of the chamber is exhausted to reduce the pressure toless than 0.01 Torr, then 20 liters/minute of Ar gas, 50 liters/minuteof hydrogen gas, and 1 liter/minute of methane gas are introduced asplasma gas to the gas introduction port 3 of the clearance between thecathode 1 and the anode 2.

Next, the pressure inside the chamber was held to 50 Torr and voltagewas supplied from the power source 4 connected between the cathode 1 andthe anode 2 to pass an arc current of 40A and generate an arc column 5between the cathode 1 and the anode 2. An attempt was made to slowlymove the cathode 1 away from the anode 2 while the arc was maintainedand raise the discharge voltage to 200 V. As a result, 200 V was able tobe realized, but this stopped in a few minutes and therefore a stabledischarge could not be obtained.

As explained above, according to the diamond producing apparatus of thepresent invention, a pilot anode was interposed in the clearance betweenthe cathode and the main anode, a main power source was connectedbetween the cathode and the main anode, an auxiliary power source wasconnected between the cathode and pilot anode, and the cathode and pilotanode were made able to move along a common axis during the discharge.

Therefore, as in the process of production of diamond of the presentinvention, a plurality of anodes are provided, the discharge is firstperformed between the cathode and the pilot anode to form plasma,whereby pilot arc is generated, and, if necessary, the cathode is movedaway from the pilot anode, the discharge voltage is maintained at apredetermined voltage, then the main arc is generated between thecathode and the main anode and thereafter the cathode and/or the pilotanode in proximity to the main anode are/is moved away from the mainanode while maintaining the discharge state, the discharge voltagebetween the cathode and the main anode is held to a predeterminedvoltage, and the plasma is jetted to synthesize diamond.

By this, using the pilot arc generated in the clearance between thecathode and the pilot anode, it is possible to prevent extinguishment ofthe main arc between the cathode and the main anode and to considerablyraise the discharge voltage between the cathode and the main anodecompared with the past.

Due to this, it is possible to stably produce high purity and highquality diamond at a high speed with a good reproducibility.

Example 8

FIG. 12 and FIG. 13 are schematic views of a three-clad anode typeplasma torch and a diamond synthesizing apparatus using this torch. Inthe figures, 40 is an electrode movement mechanism, 41 is a plasmatorch, 42 is cooling water, 43a is first gas, 43b is second gas, 43c isthird gas, 44a is a first power source, 44b is a second power source,44c is a third power source, 45 is a gas feed system, 46 is a substrateholder, 47 is a manipulator, 48 is a chamber, 49 is an exhaust system,50 is a feedstock gas introduction nozzle, and 51 is an atmospheric gasintroduction port. This torch is constructed so that the cathode 52 andthe first anode 53, the second anode 54, and the third anode 53c can bemoved during the generation of the plasma jet.

Diamond was synthesized using this apparatus by the following method.

1) The electrodes 52, 53a, 53b and 53c were placed at positions closesttogether and a 100×100×5 mm Mo substrate 19 was attached to awater-cooled substrate holder 46.

2) The inside of the chamber was exhausted to less than 0.01 Torr, then10 liters/minute of Ar was introduced as the first gas, 20 liters/minuteof hydrogen and 0.6 liter/minute of methane were introduced as thesecond gas, and 10 liters/minute of hydrogen was introduced as the thirdgas.

3) First, discharge was caused by applying a voltage across the cathode52 and the first anode 53a from the first power source 44a with a firstanode current of 20A and the cathode 52 was slowly lifted (i.e., movedaway from the first anode 53a) to make the first anode voltage 50 V.

4) Next, discharge was caused by applying a voltage between the cathode52 and the second anode 53b from the second power source 44b with asecond anode current of 40A and the cathode 52 and first anode 53a wereslowly lifted (i.e., moved away from the second anode 53b) to make thesecond anode voltage 200 V.

5) Next, discharge was caused by applying a voltage between the cathode52 and the third anode 53c from the third power source 44c with a thirdanode current of 30A and the cathode 52, the first anode 53a, and thesecond anode 53b were slowly lifted (i.e., moved away from the thirdanode 53c) to make the third anode voltage 300 V. The overall dischargeoutput became 18 kW.

6) The pressure inside the chamber was made 50 Torr and the substrateholder was brought close to the torch to make the substrate surfacetemperature 1000° C.

7) The diamond was synthesized under these conditions for one hour andthe changes in the substrate temperature were measured.

8) The synthesized diamond was examined by a scanning type electronmicroscope (SEM), the quality of the diamond was evaluated by X-raydiffraction and Raman spectroscopy, and the concentration of impuritieswas analyzed by secondary ion mass spectrometry (SIMS).

As a result, the change in the substrate temperature was less than ±10°C. The thickness of the synthesized diamond film was 400 μm, while thefilm-forming speed was 400 μm/hr. Further, the distance from the centerwhere the thickness became 80 percent (320 μm) of that of the centerportion was about 20 mm. In the X-ray diffraction, only the diamond peakwas detected, while with the Raman spectroscopy, only the diamond peakof 1333 cm⁻¹ was detected. No graphite or amorphous carbon weredetected. Further, the results of the analysis by SIMS showed that theconcentrations of tungsten and copper, which are the electrodematerials, were under 0.1 ppm.

Example 9

Diamond was synthesized by the following process using the torch of FIG.12 and the diamond synthesizing apparatus of FIG. 13 in the same way asExample 8.

1) The electrodes 52, 53a, 53b and 53c were placed at positions closesttogether and a 100×100×5 mm Mo, substrate was attached to a water-cooledsubstrate holder.

2) The inside of the chamber was exhausted to less than 0.01 Torr, then10 liters/minute of Ar was introduced as the first gas, 20 liters/minuteof hydrogen was introduced as the second gas, and 10 liters/minute ofhydrogen was introduced as the third gas.

3) First, discharge was caused by applying a voltage between the cathode52 and the first anode 53a with a first anode current of 20A and thecathode 52 was slowly lifted (i.e., moved away from the first anode 53a)to make the first anode voltage 50 V.

4) Next, discharge was caused by applying a voltage between the cathode52 and the second anode 53b with a second anode current of 40A and thecathode 52 and first anode 53a were slowly lifted (i.e., moved away fromthe second anode 53b) to make the second anode voltage 200 V.

5) Next, discharge was caused by applying a voltage between the cathode52 and the third anode 53c with a third anode current of 30A and thecathode 52, the first anode 53a, and the second anode 53b were slowlylifted (i.e., moved away from the third anode 53c) to make the thirdanode voltage 300 V. The overall discharge output became 18 kW.

6) 0.6 liter/minute of methane was introduced from the feedstock gasintroduction nozzle (50), the pressure inside the chamber was made 50Torr, and the substrate holder 46 was brought close to the torch to makethe substrate surface temperature 1000° C.

7) The diamond was synthesized under these conditions for one hour andthe changes in the substrate temperature were measured.

8) The synthesized diamond was examined by a scanning type electronmicroscope (SEM), and the concentration of impurities was analyzed bysecondary ion mass spectrometry (SIMS).

As a result, the change in the substrate temperature was less than ±10°C. The thickness of the synthesized diamond film was 400 μm and thefilm-forming speed was 400 μm/hour. Further, the distance from thecenter where the thickness became 80 percent (320 μm) of that of thecenter portion was about 25 mm. In the X-ray diffraction, only thediamond peak was detected, while with Raman spectroscopy, only thediamond peak of 1333 cm⁻¹ was detected. No graphite or amorphous carbonwere detected. Further, the results of the analysis by SIMS showed thatthe concentrations of tungsten and copper, which are the electrodematerials, were under 0.1 ppm.

Example 10

Diamond was synthesized by the following process using the torch of FIG.12 and the diamond synthesizing apparatus of FIG. 13 in the same way asExample 8.

1) The electrodes 52, 53a, 53b and 53c were placed at their respectiveclosest positions and a 100×100×5 mm Mo substrate was attached to awater-cooled substrate holder.

2) The inside of the chamber was exhausted to less than 0.01 Torr, then10 liters/minute of Ar was introduced as the first gas, 20 liters/minuteof hydrogen was introduced as the second gas, and 10 liters/minute ofhydrogen was introduced as the third gas.

3) First, discharge was caused with a first anode current of 20A and thecathode 52 was slowly lifted (i.e., moved away from the fixed anode) tomake the first anode voltage 50 V.

4) Next, discharge was caused with a second anode current of 40A and thecathode 52 and the first anode 53a were slowly lifted (i.e., moved awayfrom the fixed anode) to make the second anode voltage 200 V.

5) Next, discharge was caused with a third anode current of 30A and thecathode the first anode 53a and the second anode 53b were slowly lifted(i.e., moved away from the fixed anode) to make the third anode voltage300 V. The overall discharge output became 18 kW.

6) 0.6 liter/minute of methane was introduced from the atmospheric gasintroduction port 51, the pressure inside the chamber was made 50 Torr,and the substrate holder was brought close to the torch to make thesubstrate surface temperature 1000° C.

7) Diamond was synthesized under these conditions for one hour and thechanges in the substrate temperature were measured.

8) The synthesized diamond was examined by a scanning type electronmicroscope (SEM), and the concentration of impurities was analyzed bysecondary ion mass spectrometry (SIMS).

As a result, the change in the substrate temperature was less than ±10°C. The thickness of the synthesized diamond film was 350 μm and thefilm-forming speed was 350 μm/hour. Further, the distance from thecenter where the thickness became 80 percent (280 μm) of that of thecenter portion was about 30 mm. In the X-ray diffraction, only thediamond peak was detected, while with Raman spectroscopy, only thediamond peak of 1333 cm⁻¹ was detected. No graphite or amorphous carbonwere detected. Further, the results of the analysis by SIMS showed thatthe concentrations of tungsten and copper, which are the electrodematerials, were under 0.1 ppm.

Example 11

FIG. 14 and FIG. 15 are schematic views of two-clad anode type plasmatorch arranged coaxially in a telescoped structure and a diamondsynthesis apparatus using that torch. Diamond was synthesized by thefollowing process using the apparatus.

1) A 100×100×5 mm Mo substrate was attached to a water-cooled substrateholder.

2) The inside of the chamber 48 was exhausted to less than 0.01 Torr,then 10 liters/minute of Ar was introduced as the first gas and 20liters/minute of hydrogen and 0.6 liter/minute of methane wereintroduced as the second gas.

3) First, discharge was caused by applying a voltage between the cathode52 and the first anode 53a from the first power source 4 with a firstanode current of 20A. The discharge voltage at that time was 40 V.

4) Next, discharge was caused by applying a voltage between the cathode52 and the second anode 53b from the second power source 4 with a secondanode current of 40A. The discharge voltage at that time was 180 V. Theoverall discharge output became 8 kW.

5) The pressure inside the chamber was made 50 Torr, and the substrateholder 46 was brought close to the torch 41 to make the substratesurface temperature 1000° C.

6) Diamond was synthesized under these conditions for one hour and thechanges in the substrate temperature were measured.

7) The synthesized diamond was examined by a scanning type electronmicroscope (SEM), the quality of the diamond was evaluated by X-raydiffraction and Raman spectroscopy, and the concentration of impuritieswas analyzed by secondary ion mass spectrometry (SIMS).

As a result, the change in the substrate temperature was less than ±10°C. The thickness of the synthesized diamond film was 400 μm and thefilm-forming speed was 400 μm/hour. Further, the distance from thecenter where the thickness became 80 percent (320 μm) of that of thecenter portion was about 8 mm. In the X-ray diffraction, only thediamond peak was detected, while with Raman spectrometry, only thediamond peak of 1333 cm⁻¹ was detected. No graphite or amorphous carbonwere detected. Further, the results of the analysis by SIMS showed thatthe concentrations of tungsten and/or copper, which are the electrodematerials, were under 0.1 ppm.

Comparative Example 3

Using the torch of the conventional construction shown in FIG. 1,diamond was synthesized for one hour with 20 liters/minute of Ar, 20liters/minute of hydrogen, and 0.4 liter/minute of methane as the plasmagas, an arc current of 90A, arc voltage of 100 V, a chamber pressure of50 Torr, and a substrate surface temperature of 1000° C.

As a result, the change in the substrate temperature was +30° C. thethickness of the diamond film was 200 μm, and the distance where thethickness became 80 percent (160 μm) of the center portion was about 8mm. Further, the results of the analysis by SIMS detected tungstenand/or copper in several ppm.

Comparative Example 4

Using the conventional torch of the construction shown in FIG. 11,introducing 20 liters/minute of Ar and 20 liters/minute of hydrogen, andusing discharge current of 40A, it was attempted to raise the dischargevoltage to 200 V by slowly moving the cathode away from the anode. As aresult, 200 V could be achieved, but the discharge stopped after severalminutes and therefore a stable discharge could not be obtained.

As explained above, by using the torch of the multiclad anode of thepresent invention, the stability of the discharge is increased, thecontrollability of the substrate temperature and other synthesisconditions was improved, and the reproducibility and reliability of thesynthesis were improved. Further, the consumption of the electrodes wasreduced and the purity of the diamond increased. Also, the speed ofsynthesis was raised and the area of film formation was enlarged.

Example 12

FIG. 16 and FIG. 17 are schematic views of a three-clad anode typeplasma torch having three anodes arranged coaxially with the cathodecore provided with a deflecting magnetic field device according to thepresent invention and a diamond synthesis apparatus using this torch. Inthe figure, 54 is a cathode, 55a is a first anode, 55b is a secondanode, 55c is a third anode, 56 is an insulator, 57 is a permanentmagnet, 58 is a yoke, 59 is a coil, 60 is an arc, 61 is a plasma jet, 62is a diamond film, 63 is a plasma torch with a magnetic field generator,64 is cooling water, 65a is a first gas, 65b is a second gas, 65c is athird gas, 66a is a first power source, 66b is a second power source,66c is a third power source, 67 is a gas feed system, 68 is a substrateholder, 69 is a manipulator, 70 is a chamber, 71 is an exhaust system,72 is a feedstock gas introduction nozzle, 73 is an atmospheric gasintroduction port, 74 is a magnetic field generator power source, and 75is a substrate.

The torch has a cathode 54 and three anodes 55a, 55b, and 55c comprisedof water-cooled tungsten. The nozzle diameter of the third anode 55c is40 mm. The second and the third anodes are provided with Nd--Fe--Bsystem permanent magnets 57 treated to prevent rusting. The magneticfield of the permanent magnets 57 is applied in the axial direction ofthe torch to promote rotation of the anode point. A total of fourelectromagnets for generating a deflecting magnetic field are disposedin the X and Y two directions. The coil is water-cooled. The powersource for the magnetic field generator is comprised of X, Y two systemAC power sources with phases differing by 90° and a variable frequency.These can be changed in output current independently. The magnetic fluxdensity generated was a maximum 1000 Gauss at the center axis.

The water-cooled copper substrate holder is positioned on a manipulatormovable in the XYZ directions. The chamber is of a two-layerwater-cooled construction and is connected to a mechanical booster pumpand rotary pump. There are gas feed ports at three locations in thetorch and two locations at the torch outlet and the chamber wall.Usually, Ar is fed as the first gas, hydrogen as the second gas, andhydrogen as the third gas. Methane, the source of the carbon, is fedfrom the five feed ports in accordance with need.

As the substrate, use is made of an Mo substrate of 100×100×5 mm. Adiamond film is synthesized on the surface by the following procedure.

1) The inside of the chamber was exhausted to less than 0.01 Torr, then10 liters/minute of Ar was introduced as the first gas, 20 liters/minuteof hydrogen and 0.6 liter/minute as the second gas, and 10 liters/minuteof hydrogen as the third gas.

2) First, discharge was caused at a first anode current of 20A byapplying a potential between the cathode 54 and the first anode 55a.

3) Next, discharge was caused at a second anode current of 40A byapplying a potential between the cathode 54 and the second anode 55b.

4) Next, discharge was caused at a third anode current of 60A byapplying a potential between the cathode 54 and the third anode 55c. Theoverall discharge power at this time became 20 kW.

5) The deflecting magnetic field generator was operated to generate amagnetic field with a frequency of 100 Hz and a peak magnetic fluxdensity of 500 Gauss.

6) The pressure in the chamber was made 50 Torr and the torch wasbrought close to the substrate holder to make the substrate surfacetemperature 1000° C.

7) Diamond was synthesized under these conditions for one hour.

8) The synthesized diamond was examined by a scanning type electronmicroscope (SEM), the quality of the diamond was evaluated by X-raydiffraction and Raman spectroscopy, and the concentration of impuritieswas analyzed by secondary ion mass spectrometry (SIMS).

FIG. 18 shows the distribution of thickness of the synthesized diamondfilm. Further, for comparison, FIG. 18 also shows the distribution ofthickness in the case of synthesis of diamond under the same conditionsas Example 11 except that no deflecting magnetic field was applied.Without the deflecting magnetic field, the area of film formation wasabout 40 mm diameter with the center portion being thicker, while withthe application of the deflecting magnetic field, a substantiallyuniform thickness was obtained over an approximately 60 mm diameter. Alook at the speed of film formation shows that the speed of filmformation at the center portion fell due to the application of themagnetic field, but that there was almost no change when viewed in termsof the speed of film formation by volume. Further, in the X-raydiffraction, only the diamond peak was detected, while with Ramanspectroscopy, only the diamond peak of 1333 cm⁻¹ was detected. Nographite or amorphous carbon were detected. Further, the results of theanalysis by SIMS showed that the concentration of tungsten, theelectrode material, was under 0.1 ppm.

Example 13

FIG. 19 and FIG. 20 are schematic views of a two-clad anode type plasmatorch having two anodes arranged coaxially with the cathode coreprovided with a deflecting magnetic field device according to thepresent invention and a diamond synthesis apparatus using this torch. Inthe figure, 76 is a cathode, 77a is a first anode, 77b is a secondanode, 78 is an insulator, 79 is a permanent magnet, 80 is a yoke, 81 isa coil, 82 is an arc, 83 is a plasma jet, 84 is a diamond film, 85 is aplasma torch with a magnetic field generator, 86 is cooling water, 87ais a first gas, 87b is a second gas, 88a is a first power source, 88b isa second power source, 89 is a gas feed system, 90 is a substrateholder, 91 is a manipulator, 92 is a chamber, 93 is an exhaust system,94 is a feedstock gas introduction nozzle, 95 is an atmospheric gasintroduction port, 96 is a magnetic field generator power source, and 97is a substrate.

The torch has a cathode 76 and two anodes 77a, 77b comprised ofwater-cooled tungsten. The nozzle diameter of the second anode is 5 mm.The second anode 77b is provided with an Nd--Fe--B system permanentmagnet treated to prevent rusting. The magnetic field is applied in theaxial direction of the torch to promote rotation of the anode point. Atotal of four electromagnets for generating a deflecting magnetic fieldare disposed in the X and Y two directions. The coil is water-cooled.The power source for the magnetic field generator is comprised of X, Ytwo system AC power sources with phases differing by 90° and a variablefrequency. These can be changed in output current independently. Themagnetic flux density generated was a maximum 1000 Gauss at the centeraxis.

The water-cooled copper substrate holder is positioned on a manipulatormovable in the XYZ directions. The chamber is of a two-layerwater-cooled construction and is connected to a mechanical booster pumpand rotary pump. There are gas feed ports at two locations in the torchand two locations at the torch outlet and the chamber wall. Usually, Aris fed as the first gas and hydrogen as the second gas. Methane, thesource of the carbon, is fed from the four feed ports in accordance withneed.

As the substrate, use is made of an Mo substrate of 100×100×5 mm. Adiamond film is synthesized on the surface by the following procedure.

1) The inside of the chamber was exhausted to less than 0.01 Torr, then10 liters/minute of Ar was introduced as the first gas, 20 liters/minuteof hydrogen as the second gas, and 0.4 liter/minute of methane as thestarting gas.

2) First, discharge was caused at a first anode current of 20A byapplying a potential between the cathode 76 and the first anode 77a.

3) Next, discharge was caused at a second anode current of 100A byapplying a potential between the cathode 76 and the second anode 77b.The overall discharge power at this time became 15 kW.

4) The deflecting magnetic field generator was operated to generate amagnetic field with a frequency of 100 Hz and a peak magnetic fluxdensity of 500 Gauss.

5) The pressure in the chamber was made 50 Torr and the torch wasbrought close to the substrate holder to make the substrate surfacetemperature 1000° C.

6) Diamond was synthesized under these conditions for one hour.

7) The synthesized diamond was examined by a scanning type electronmicroscope (SEM), the quality of the diamond was evaluated by X-raydiffraction and Raman spectroscopy, and the concentration of impuritieswas analyzed by secondary ion mass spectrometry (SIMS).

FIG. 21 shows the distribution of thickness of the synthesized diamondfilm. Further, for comparison, FIG. 21 also shows the distribution ofthickness in the case of synthesis of diamond under the same conditionsas Example 12 except that no deflecting magnetic field was applied.Without the deflecting magnetic field, the area of film formation wasabout 30 mm diameter with the center portion being thicker, while withthe application of the deflecting magnetic field, a substantiallyuniform thickness was obtained over an approximately 40 mm diameter. Alook at the speed of film formation shows that the speed of filmformation at the center portion fell due to the application of thedefecting magnetic field, but that there was almost no change whenviewed in terms of the speed of film formation by volume. Further, inthe X-ray diffraction, only the diamond peak was detected, while withRaman spectroscopy, only the diamond peak of 1333 cm⁻¹ was detected. Nographite or amorphous carbon were detected. Further, the results of theanalysis by SIMS showed that the concentration of tungsten, theelectrode material, was under 0.1 ppm.

By using the deflecting magnetic field applying torch of the presentinvention, it is possible to increase the area of irradiation of theplasma jet and increase the area of synthesis of the diamond.

Example 14

As shown in FIG. 22, first, the inside of the chamber 98 was exhaustedby the vacuum pump 99 to about 10⁻² Torr. After this, 10 liters/minuteof Ar was introduced as the first gas, 20 liters/minute of hydrogen and0.6 liter/minute of methane as the second gas, and 10 liters/minute ofhydrogen as the third gas (gas system 110).

The pressure inside the chamber 98 was made 50 Torr and the DC powersource 100 was used to start discharge at a first anode current of 20A,a second anode current of 40A, and a third anode current of 30A. In thetorch was placed a permanent magnet 101 so as to generate a magneticfield downward with the cathode as the axial line. The magnetic field atthe front end of the torch was measured at this time and found to be2000 Gauss. The plasma jet 102 was irradiated on to the substrate fixedon the water-cooled substrate holder 103 from the front end of theplasma torch, whereby diamond was produced.

The stability of the discharge can be examined by the voltage across theanodes and cathode, that is, the discharge voltage. Examination of thechange of the discharge voltage over time gave the results shown in FIG.23. That is, it was learned that the discharge voltage was equalized andstabilized.

Example 15

As shown in FIG. 24, first, the inside of the chamber 104 was exhaustedby the vacuum pump 105 to about 10⁻² Torr. After that, 10 liters/minuteof Ar was introduced as the first gas, 20 liters/minute of hydrogen and0.6 liter/minute of methane were introduced as the second gas, and 10liters/minute of hydrogen was introduced as the third gas.

The pressure inside the chamber 104 was made 50 Torr and the DC powersource 106 was used to start discharge at a first anode current of 20A,a second anode current of 40A, and a third anode current of 30A. At thesame time as this, the outermost arranged third anode electrode wasrotated at 60 rpm by the anode rotation motor 107. The plasma jet 108was irradiated on to the substrate fixed on the water-cooled substrateholder 109 from the front end of the plasma torch, whereby diamond wasproduced. Note that 110 shows the gas system.

The stability of the discharge may be investigated using the voltageacross the third anode and cathode, that is, the discharge voltage. Ifthe change of the discharge voltage over time is investigated, one getsFIG. 25. That is, it was learned that the discharge voltage wasequalized and made stable.

Further, a similar effect can also be obtained by moving the cathode.

We claim:
 1. A process for producing diamond, comprising the steps of:(a) bringing both a columnar cathode and a tubular pilot anode, provided concentrically around said cathode set apart with a clearance from said cathode, into proximity to a plasma jetting port of a front end portion of a tubular main anode, provided concentrically around said pilot anode set apart with a clearance from said pilot anode, (b) applying a discharge voltage across said cathode and said pilot anode to convert a pilot gas introduced in the clearance between said cathode and said pilot anode to a plasma, (c) after step (b), moving the cathode which is close to said pilot anode away from said pilot anode along a common axis, (d) holding the discharge voltage across said cathode and said pilot anode to a first preselected voltage, (e) after step (d), applying a discharge voltage across said cathode and said main anode to convert a main gas introduced in the clearance between said main anode and said pilot anode to a plasma, (f) after step (e), moving at least the pilot anode which is close to the main anode away from the main anode along said common axis while maintaining the discharge voltage across said cathode and said pilot anode at the first preselected voltage, (g) holding the discharge voltage across said cathode and said main anode to a second preselected voltage, and (h) jetting the main gas in the form of plasma from said jetting port toward a substrate while generating a main arc between said main anode and said cathode and maintaining the second preselected voltage, thereby producing diamond on the substrate.
 2. A process as set forth in claim 1, wherein said pilot gas is argon gas or another inert gas and said main gas is a mixed gas of hydrogen gas or an inert gas and a gas comprised of a carbon compound used as a feedstock gas.
 3. A process as set forth in claim 1, which introduces a gas including a feedstock gas into the plasma jet from the plasma jetting port of said main anode.
 4. A process as set forth in claim 3, wherein said pilot gas is argon gas or another inert gas, said main gas is hydrogen gas or an inert gas, and said feedstock gas is a gas comprised of a carbon compound.
 5. A process as set forth in claim 1, wherein said diamond is produced in a chamber having a reduced pressure, and atmospheric gas is introduced into said chamber from a gas introduction port in a wall of said chamber.
 6. A process as set forth in claim 5, wherein said pilot gas is argon gas or another inert gas, said main gas is hydrogen gas or an inert gas, and said atmospheric gas is a gas comprised of a carbon compound.
 7. A process as set forth in claim 5, wherein said pilot gas is argon gas or another inert gas, said main gas is hydrogen gas or an inert gas, and said atmospheric gas is a mixed gas comprised of a gas comprising a carbon compound, an oxidizing gas, a halogen gas, and a halogenated hydrogen gas. 